Riri could not believe what she was hearing when the audience member - now identified as choir-trained Terah Stewart - showed off his unbelievable vocal talents during her show at the US Bank Arena in Cincinnati.

The superstar songstress held the microphone in front of Terah's face during her Anti World Tour and got more than she bargained for when he belted out 2015 hit FourFiveSeconds.

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(Image: Twitter)

Check out the look on Rihanna's face!

The Umbrella hitmaker eventually went back to singing but she was clearly still shocked to have stumbled upon such a talent right under her nose.

(Image: Twitter)

A video of the impromptu sing-along has been shared thousands of times after being posted online.

The general consensus is that the fan stole the show and that it won't be long until he's selling out arenas himself.

(Image: Twitter)

One person joked: "Riri took that microphone back real quick before he snatches her career."

Another wrote: "I would love him to do the whole song that's so good."

(Image: Twitter)

Meanwhile Terah himself tweeted: "Y'all don't understand how long I have been riding for @Rihanna. I will never forget this. She followed me too. #NavyForF***ingLife!!!!!!!"

Terah, who also got to sing part of the second verse, is reportedly hoping that his brief moment in the limelight could land him a job on Broadway, according to TMZ.

Rihanna's tour has been newsworthy in more ways than one thanks to Drake joining her on stage.

The pair, who are rumoured to be dating, simply ooze chemistry whenever they're side by side.